Keying



Aug. 10, 1937. PRAY 2,089,811

KEYING Original Filed Nov. 19, 1930 3 Sheets-Sheet l r0 RF. arc/Aura? 2 70 RE OSCILLATOR 7 INVENTOR G. E 1 /34) ATTO R N EY G. E. PRAY KEYING Aug. 10, 1937.

Original Filed NOV. 19, 1930 3 Sheets-Sheet 3 INVENTOR 6. E. PRAY ATTORNEY Patented Aug. 19, 1937 George Emerson Pray, Gceanport, N. J., assigncr to Radio Corporation of America, a corporation of Delaware Original application November 19, 1930, Serial Divided and this application April 28, 1934, Serial No. 722,829

9 Claims.

This invention relates to transmitters and in particular to a novel method of and means for keying transmitters including a method of and means for eliminating key shocks heretofore present in transmitters. This application is a division of Prays United States application No. 496,622 filed November 19, 1930, Patent #1,9'77,596, October 16, 1934.

It is well known that when a radio receiver or radio receiving equipment is mounted in the vicinity of a transmitter the reception of signals in said. receiver is interfered with more or less by disturbances originating in the transmitter. In each keying operation of the transmitter the rise and fall of the signal current in the circuits thereof is audible in a receiver adjacent thereto in the form of a crackling noise known in the art as key clicks or key shocks. The nearer the transmitter is to the receiver the greater is the interference caused by the transmitter in the received signals. If the transmitter is located in the same room or close to the receiver then reception of signals in the receiver becomes practically impossible during the time in which the transmitter is operating.

Attempts have been made heretofore to eliminate disturbances in receiving circuits which originate in a transmitter located adjacent thereto. One method used heretofore to eliminate such disturbances in the receivers involves the use of shielding for the receiver and/or for the transmitter. Another method contemplates the use of radiofrequency choke coils in the receiver and/or transmitter circuits. Generally such at- 35 tempts have been more or less unsuccessful due to the fact that when the first method is used theshielding effect is not complete and when the second method is used complete elimination is not obtained since the initial stage of the oscillations 40 in the transmitter due to keying contains a practically continuous frequency band or spectrum. Choke coils used for this purpose would block out a single frequency or a narrow band of frequencies. Oscillations of other frequencies would en- 45 ter the radio receiving circuits and cause disturbances therein.

The object of the present invention is to provide a novel method of and means for eliminating at the source, that is in the transmitter, disturb- 50 ances which may affect radio receiving apparatus and which are due to keying operations of the transmitter.

Another object of the present invention is to provide a novel method of and means for elimi- 55 hating keying disturbances at the source, that is in the transmitter, in which the keying apparatus operates at a low potential whereby the disturbances to be eliminated are of low amplitude.

Numerous other objects will become apparent from a reading of the specification.

Briefly and broadly the above objects are obtained by the use of a keying system for transmitters which includes means to prevent the sudden rising of the keying current at the start of the keying operation and the abrupt falling oif thereof at the termination of the keying operation. This results in key signals, the sharp edges of which are, as it were, rounded off.

In one modification of the invention the keying means involves the use of a keying tube having its anode connected to the screen grid electrode of one of the tubes in the high frequency generator, and its input circuit connected in a novel manner to a source of potential through a filter network, the elements of which are proportioned to retard a change in the input current due to sudden changes of potential on the grid of the keying tube and consequently retard the initial and final changes in the keying current and potential appearing on the anode of said keying tube.

A further modification involves an arrangement in which the input circuit of the keying tube including the filter network is somewhat similar to the input circuit and filter network of the keying tube described above but in which the anode circuit of the keying tube is connected to the anode circuit of one of the tubes of the transmitter in such a manner that the keying potentials, the corners of which are rounded off as hereinbefore described, are applied to the anode of said transmitter to modulate the frequencies generated or amplified therein.

In the above described modifications the keying potential for the input of the keying tube is obtained by the use of a battery having opposed terminals connected together and tothe filament of the keying tube while the other terminals thereof are connected to contacts cooperating with the key in such a manner that negative and positive potentials may be alternately applied to the control electrode of the keying tube.

Still another arrangement is provided wherein the keying impulses which are applied to the control electrode of one of the transmitter tubes, are obtained by a keying tube, the input circuit of which is connected with a resistance supplied with potential from any source, which resistance supplies the anode cathode and control electrode potential for the keying tube, and the control electrode potential for the transmitter tube. A second source of potential supplies the anode potential and screen grid potential for the transmitter tubes.

Provision has also been made whereby the last referred to embodiment may be entirely supplied with current from a single source.

The novel features of applicants invention will be pointed out specifically in the claims attached hereto. A better understanding of the invention and the operation thereof will be had from the following detailed description thereof and therefrom when read in connection with the attached drawings throughout which like reference numerals indicate like parts.

Figure 1 shows one embodiment of applicants novel keying means and its application to a transmitter;

Figures 2 and 3 show modifications of the arrangement of Figure 1;

Figure 3a shows novel means whereby the arrangement of Figure 3 may be energized by a single source; while Figures 4a to 4d show curves characteristic of the currents flowing in certain ones of the circuits of the hereinbefore described arrangement.

Referring to the drawings and in particular to Figure 1 thereof, I is a thermionic amplifier or osciliaticn generator having its input circuit 2 connected to a source of oscillation 3 and its output tank circuit 4 connected to a load circuit 5. The oscillation generator or amplifier in itself forms no part of the present invention. A detailed description thereof is deemed unnecessary except to state that the frequency of the input circuit 2 may be determined by the tuning capacity shown therein While the output circuit of I includes a blocking condenser E, and a tuned tank circuit as shown. Potential is supplied to the screen grid and the anode of thermionic tube I from a source B+ (not shown) through resistance R2 and choke coil H respectively. The purpose of resistance R2 is to reduce the potential reaching screen grid I while the purpose of the choke coil H is to prevent high frequency oscillations appearing on the anode of I from reaching the source 13+.

In order that the oscillations appearing in the anode circuit of i may be modulated at signal frequency the screen grid electrode I of tube I is connected to the anode 8 of the keying tube9 in such a manner that potential from B through R2 supplies the anode cathode circuit of tube 9, as well as the screen grid 1 of tube I. The potential of the anode 8 and the direct current flowing in the anode cathode circuit of tube 9 will vary at signal frequency as will appear in detail hereinafter. This variation will be utilized to key thermionic tube I. The variations will start and terminate slowly in accordance with the present invention, thereby eliminating key clicks heretofore present in transmitters of this type.

In order that the potential appearing at 8 and the current flowing in the anode circuit of 9 may vary at signal frequency the input circuit I9 of tube 9 includes a key K adapted to connect the grid I I of tube 9 through a resistance R1 either to the negative or positive terminal of battery E, the midpoint of which is connected, as indicated, to the'filarnents of tubes I and 9, whereby manipulation of the key K will apply to the grid II a potential either negative or positive with respect to the filament of the tube 9. When the key K connects the grid I l of tube 9 to the negative terminal of battery E the tube 9 is nonconducting and since no current can flow between the anode 8 of tube 9 and the cathode a high potential is applied 7 to the screen grid l of tube I. This is due to the fact that the anode cathode circuit of tube 9 and the screen grid cathode circuit of tube l are supplied with direct current through a common circuit R2, B+. When the control grid of tube 9 is connected to the positive terminal of the battery E tube 9 becomes conductive and anode cathode current fiows therein. This absorbs current from the screen grid cathode circuit of tube I. This tends to decrease the potential at I.

Up to this point applicant has described a novel and efiicient keying method in which reverse keying is obtained and in which keying shocks and key clicks are substantially reduced due to the inherent characteristics of the circuit. However, in order to further insure that the keying potentials on the anode 8 do not rise and fall at too rapid a rate the electrical inertia is applied in accordance with the present invention to the input circuit of tube 9 and to the output circuit thereof in the form of a resistance R1, a condenser C1, a resistance R2 and acondenser C2. In actual practice it has been found that the condenser C1 may, and often does, comprise the capacity between the control electrode and cathode of tube 9. Filament heating current is supplied to the filaments of tubes i and 9 from a common source of potential A, as shown while negative potential is supplied to the grid of I from a source G.

The arrangement shown in Figure 2 is somewhat similar to the arrangement of Figure 1, The arrangement of Figure 2 differs from the arrangement of Figure 1 in several respects. In Figure 2 the anode cathode circuit of keying tube 9 derives its current and potential from the same circuit which supplies current and potential to the anode and cathode circuit of tube I, thereby producing anode modulation at signal frequency, which is reversed with respect to the keying operations while the inertia necessary to round oif the sharp corners of the keying modulation is obtained by resistance R1, condenser C1 and resistance R1; and condenser C3.

In order that the keying potential may be applied to the control electrode of one of the tubes of the transmitter, the arrangement of Figure 3 has been provided. In this arrangement the biasing potential for the control electrode of tube i, and the anode potential and the control grid electrode potential for the keying tube 9 are supplied from a single resistance, which may be connected across any source of direct current potential LV. The anode cathode and screen grid cathode potential for the amplifier I is supplied from a separate high voltage source HV. In this arrangement the potential of the control electrode it of tube I is determined by the current which fiows in the anode cathode circuit of the key tube 9 since the anode cathode current in the tube 9 is made up of the rectified current in the grid cathode circuit of i and of the current due to the volta e dropped across Re When the key K'supplies a negative potential to the control grid II through R1 the tube 9 is nonconducting and since no current can fiow in the anode cathode circuit thereof the potential supplied to I E is negative, that is, more negative than normal, and the oscillations generated or amplified in I are cut off. When the key K connects the control grid iI to a positive point on resistance R4, that is, a point more positive than normal, the keying tubes becomes conductive and current flows in the anode cathode circuit thereof. This permits rectified current to flow in the grid cathode circuit of tube l, causing the potential applied to the grid l2 of tube l to become less negative, making the tube conductive, and allowing current to flow in the anode cathode circuit thereof. In this modification the keying operation is simultaneous in the keying and in the keyed circuits. The current in the radio frequency circuit, that is, the output circuit of tube l, will follow the same curves as that oi the keying circuit it and in the input circuit or the keying tube 9. In the apparatus, as arranged in accordance with applicants novel invention shown in Figure 3, the current fiowing in the output of 8 and in the input circuit of i will lag the keying operations due to the inherent nature of the circuits. This in itself will tend to round off the corners of the keying current, thereby eliminating key shocks and key clicks from being produced by the circuits. In order to further insure that the current due to keying does not rise or fall too rapidly additional time lag characteristics are obtained by providing additional inertia in the form of resistance R1, condenser C1 and resistance R4 and condenser C4. The condensers it and iii tend to eliminate any potential variations appearing in R4 at audio frequency and preventing such varia tions from affecting the signals to be transmitted. It will be noted in this modification that separate sources of potential are required for the filaments of i il in order that the keying currents therein be confined to the proper circuits so that the anode cathode circuit of tube 9 will carry the rectified current flowing in the grid circuit of l in addition to current flowing therein due to potential drop across resistance R4.

In Figure 3a is shown a keying arrangement which may be applied to the input circuit of keying tube a and which permits the use of a single source of potential to operate both tubes. In this arrangement, the potential necessary for the entire operation of the apparatus including the radio frequency tubes and the keying tube 9 is obtained from a resistance R4, R5 adapted to be connected across a source of high potential I-lV not shown. Keying potential for the control grid l l of keying tube 9 is supplied through a resistance R1 connecting said grid when the key K is in the open position to the negative terminal of the resistance R4 and when the key K is close to a predetermined point on B4, which .s positive with respect to the negative terminal OfRA. In this manner the keying tube 9 can be rendered conductive or nonconductive by manipulation of the key K1. The control electrode of radio frequency tube l is connected as in Figure 3 to a point on resistance R4 so that the potential applied to the grid l2 of i may be varied at signal frequency in a manner somewhat similar to that in which it is varied in the modification shown in Figure 3. In this arrange-, ment manipulation of K1 varies the bias applied to the grids of tubes 9 and 5 between the limits of some predetermined negative values of voltage. The anode cathode current flowing in the keying tube 9 is, as in Figure 3, the sum of the rectified grid current flowing in tube 1 and the current flowing due to the potential drop across R4. Since the current which could flow in the anode cathode circuit of the keying tube 9 depends on the conductivity of the tube the poten- V tial applied to the grid l2 will depend upon the portion of the anode cathode current for the radio frequency tube. This condition occurs due to the fact that keying tube El offers a relatively low resistance path for the return of anode cathode current from the cathode of tube l to the negative side of the high voltage. This results in no serious disadvantage but does result in a change in the form of the keying wave.

In connection with Figures 1 and 2, it will be understood that although separate sources of tential have been shown to energize the elements of the several tubes, all of the elements of the tubes may be energized from a single source. In the arrangements of Figures 3 and 80:, separate sources of potential are used for the filaments of tubes l and 9.

In explaining the operation of the several modifications reference will be had to Figs. 4a to 4d of the drawings in which curves are shown representative of the current flowing in various circuits of the tubes plotted with reference to time. The operation of the keying circuits shown in Figures 1, 2 and 3 is the same, and a statement of the operation of Figure 1 will be sufficient to explain the operation of all of these modifications. Referring to Figures 1, 2 and 3, and the curves of Figs. 4a to 4d, assume that the keying relay K connects the negative terminal of the battery E to the grid ii of keying tube 9 so that a suificiently negative voltage is supplied as a straight line to the proper positive value,

as indicated by the dotted line Egi, curve of Figure 4a, the anode cathode current of 5 would then follow the curved dotted line I'p as shown by the dotted line in curve of Figure 4b. No practical scheme, however, has yet been devised to permit variation of the grid bias in a straight line to obtain the desirable result indicated in curve of Figure 4b. The next best solution which has been devised in accordance vnlth the present invention is to use filter circuits to introduce sufficient lag in the circuits to accomplish the above result. These circuits have been found to give very goods results. While the keying relay K is in the position indicated above C1 receives a negative charge. If the relay K now moves to its other position wherein the battery E tends to apply a positive potential to the grid l, C1 starts to discharge through R1 and after it has discharged starts to charge positively through R1 and then the grid H receives a positive bias. The grid voltage curve obtained by the use of this filter network is shown by the full line curve Eg of Figure 4a. The resulting anode cathode current appearing in keying tube 9 is shown by the full line curve Ip of Figure 41).

When the keying relay K returns to its first position connecting the grid l l through resistance R1 to the negative terminal of battery E, C1 discharges through the tube and through R1 and then charges negatively through R1 and allows the grid H of tube 9 to receive a negative bias. The curve E9! of C shows the fall of potential of the grid ll of tube 9 when K connects said grid to the negative terminal of the battery E, which would result if the potential could be caused to fall as a straight line. The actual fall of the current on the grid Eg, as obtained by the use of the applicants filter network or lag introducing circuit, is shown by the full line curve Eg of Figure 4c. The anode cathode current which would appear in the output circuit of tube 9 if the potential on the grid thereof could be controlled in accordance with Eg of curve of Fig. 4c, is indicated at 1'1) of curve of Fig. id, while the current actually obtained in the anode cathode circuit of tube 3 is indicated by the full line Ip in curve of Figure 401.

In the arrangement shown in Figure 3a, the keying relay K varies the bias on grid H between the limits of some predetermined negative values of voltage, limiting the maxi-mum value of Ip to some point on the straight line portion of the 1p curve. This reduces the time factor due to the upper portion of 1;!) of curve of Figure ib and causes this curve to flatten out sooner, thereby giving lower maximum but more abrupt curves at the top corners of the keying wave. This is likewise a characteristic to a lesser extent of the modification shown in Figures 1, 2 and 3, especially ii the keying relays were to be replaced by one similar to K of Figure 3a.

Having thus described my invention and the operation thereof, what I claim is:

1. In a signalling system, a high frequency thermionic tube relay, a thermionic modulator tube, a circuit connecting the anode to cathode impedance of the modulator tube in series with the control grid to cathode impedance of the relay tube, a potentiometer adapted to be connected with a source of potential, circuits connecting said i-mpedances in parallel with a portion of the resistance in said potentiometer, a pair of contacts connected with the resistance in said potentiometer, a key cooperating with said contacts, a keying circuit, and a filter circuit connecting said keying circuit to the control grid and cathode of said modulator tube.

2. In a signalling system, a high frequency thermionic tube relay and a thermionic modulator tub-e, each of said tubes having an anode, a cathode and a control grid, a circuit connecting the anode to cathode impedance of the modulator tube in series with the control grid to cathode impedance of the relay tube, a potentiometer resistance adapted to be connected with a source of direct current potential, circuits connecting said tube impedances in parallel with a portion of the resistance in said potentiometer, a key, contacts cooperating with said key and connected with said potentiometer resistance to connect said key to different points on said resistance, a filtering circuit connected with said contacts and said resistance, a keying circuit connecting said key to the control grid of said modulator tube, and a filter circuit connected between said key and the control grid and cathode of said modulator tube.

3. In a signalling system, a high frequency thermionic tube relay, a thermionic modulator tube, each of said tubes having an anode, a cathode and a control grid, a circuit connecting the anode to cathode impedance of the modulator tube in series with the control grid to cathode impedance of the relay tube, a potentiometer resistance adapted to be connected with a source of potential, circuits connecting said impedances in parallel with a portion of the resistance in said potentiometer, a key connected with the control grid of said modulator tube, a pair of contacts cooperating with said key and connected to different points on the resistance of said potentiometer, a resistance between. said key and said control grid, and a condenser between the control grid and cathode of said tube.

i. A device as recited in claim 2 in which said first named relay tube has an additional electrode and in which the anode electrode of said relay tube and said additional electrode are connected with said resistance.

5. A signal system as recited in claim 3 in which a capacitive element is connected in shunt with said contacts.

6. In a telegraph system, a thermionic relay tube having a control grid and a cathode, a thermionic modulator tube having an anode, a control grid, and a cathode, a source of direct current potential, 2. direct current circint connecting the control grid to cathode impedance of the relay tube and the anode to cathode i npedance of the modulator tube in series, a circuit connecting said impedances in parallel with a portion of said source of direct current potential, a key, a resistance connecting said key to the control grid of said modulator tube, and a pair of contacts connected to points of different potential on said source of direct current potential, said contacts cooperating with said key when manipulated to apply difierent direct current potentials to said control grid by way of said resistance.

7. A system as recited in claim 6 in which capacitive means is connected between said contacts.

8. A system as recited in claim 6 in which, a capacity is connected between the control grid and cathode of said modulator tube.

9. A system as recited in claim 6 in which, a capacity element is connected in shunt with said contacts, and in which, a condenser is connected between the control grid and cathode of said modulator tube. V

G. EMERSON PRAY. 

